This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 98-16786 filed in Korea on May 11, 1998; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a very high speed digital subscriber line (VDSL) receiver, and a programmable gain amplifier (PGA) and a narrow-band noise remover thereof, and more particularly, to a VDSL receiver for controlling gain during reception of a signal including narrow-band noises, and a PGA and a narrow-band noise remover thereof.
2. Description of the Related Art
As the need for information transmission increases, there has been much research conducted to find a method for transmitting data at high speed. In particular, research has concentrated on a method utilizing conventional telephone lines to transfer information at a high speed.
VDSL is a technology for transferring data at a high speed to subscribers over conventional telephone lines eliminating the need for selection of a specific pair of lines and which does not require particular conditions or a redesign of the conventional telephone lines. In the VDSL, data streams consist of high-speed data 20 such as compressed video data, going toward subscribers from an information source, and high-speed data such as a control signal, going toward the information source from the subscriber.
A VDSL system, as shown in FIG. 1, comprises a VTU-O (VDSL Transmission Unit at the Optical Network Unit) 100 for transmitting data to subscribers and receiving data from the subscribers, and a VTU-R (VDSL Transmission Unit at the Remote Location) 102 connected through a channel to the VTU-O, for transmitting data to the information source and receiving data therefrom. During data transmission through the channel between the VTU-O 100 and the VTU-R 102, AWGN (Additive White Gaussian Noise) and narrow-band noise intrudes.
The AWGN refers to the noises distributed over a wide frequency band with a relatively small amplitude, and narrow-band noise refers to the noises generated at a narrow frequency band with a high amplitude and causing serious errors to a s receiving site. The narrow-band noise can be in the form of an RFI (Radio Frequency Interference) or an impulsive noise. RFI is signal interference from ham radio communications. According to the characteristics of the RFI, generation of such signals is not continuous. That is, the signals are randomly generated or disappear over several milliseconds to several seconds. Also, the generated signal occupies an arbitrary frequency band, thus it is a major interference factor compared to a general broadcast wave. On the other hand, in the case that impulsive noise is generated when a fluorescent lamp is turned on, its interference duration lasts several microseconds, which is too short and thus negligible.
FIG. 2 is a block diagram of a conventional VDSL. The VDSL comprises an automatic gain controller (AGC) 200, an equalizer 202 and a slicer 204.
The conventional VDSL of FIG. 2 operates as follows. The AGC 200 controls the power of an input signal to a desired level, and the equalizer 202 compensates for deteriorated characteristics of the signal output from the AGC 200. The slicer 204 converts the output of the equalizer 202 into a digital value according to a threshold value.
FIG. 3 is a detailed block diagram of the AGC 200 of FIG. 2. The AGC 200 comprises a multiplier 300, an analog-to-digital converter (ADC) 302, a mean square calculator (MSC) 304, an adder 306, an integrator 308 and a gain regulator 310.
The AGC 200 operates as follows. First, the multiplier 300 multiplies the input signal by a feedback gain-controlled value. The ADC 302 converts the output of the multiplier 300 into a digital signal and outputs the digital signal. The MSC 304 calculates the mean power to the output signal of the ADC 302. The adder 306 calculates the difference between the mean power and a reference power level, and the integrator 308 integrates the output of the adder 306, which is for making the signal insensitive to surrounding noises. The gain regulator 310 compares the output of the integrator 308 with a threshold value to output a gain control value according to the comparison back to the multiplier 300.
The main function of the above-described AGC is to provide a desired power level to the input signal. Thus, the requirements of a device such as a synchronizer which requires an input signal to be a predetermined step size or belong to a predetermined dynamic range of a receiving site may be not satisfied. Also, the conventional AGC controls the gains to a predetermined amplitude regardless of surrounding interference signals, so that it cannot cope with sudden changes in power due to major interference factors such as RFI. Accordingly, it is not possible to process the error generated by a sudden surge or drain of power. For example, when only a signal is input during initialization of a system, the AGC controls the gain only based on the input signal. Here, when an RFI signal having a power equivalent to the original signal is input suddenly, the power of all signals is doubled. Accordingly, when the signals pass through the ADC, the original signal is clipped, thereby causing quantization error.
Also, when strong narrow-band noise such as RFI intrudes into transmission lines, the performance of the conventional receiver deteriorates. As a result, desired performance of the entire system cannot be realized, When the amplitude of the narrow-band noise is very large, the operation at the receiving site becomes unstable, and the tap coefficient of an equalizer of the receiving site diverges such that transmitted data cannot be detected. Also, because no one can predict when, at what amplitude and into which frequency narrow band noise will intrude, it is not possible to adaptively remove the narrow-band noise.
To solve the above problems, it is an object of the present invention to provide a programmable gain amplifier (PGA) for maintaining the amplitude of an attenuated or distorted signal input to a receiving site of a very high speed digital subscriber line (VDSL) system at a desired level, narrow-band noise remover for removing narrow-band noises mixed in the input signal, and a VDSL receiver having the same.
According to an aspect of the present invention, there is provided a very high speed digital subscriber line (VDSL) receiver for processing an input signal to which a narrow-band noise is inflowed, for high-speed transmission, the receiver comprising: a first programmable gain amplifier (PGA) for controlling gain to output a signal having a predetermined amplitude and amplifying the input signal according to the controlled gain; a narrow-band noise remover for detecting the narrow-band noise from the output signal of the first PGA, modeling the narrow-band noise to remove the noise from the output signal of the first PGA if the narrow-band noise is detected, and outputting the inherent output signal of the first PGA if the narrow-band signal is not detected; a second PGA for amplifying the output signal from the narrow-band noise remover based on the gain controlled by the first PGA if narrow-band noise exists, and outputting the inherent output signal of the narrow-band noise remover without amplification if narrow-band noise is not detected; an equalizer for compensating for the deteriorated characteristics of the output signal from the second PGA; and a slicer for converting the output signal of the equalizer into a digital signal.
According to another aspect of the present invention, there is provided a programmable gain amplifier (PGA) for controlling a gain to amplify an input signal, comprising: a multiplier for multiplying the input signal by a feedback signal; an analog-to-digital converter (ADC) for converting the output of the multiplier into a digital signal, and outputting the digital signal; a peak detector and averager for detecting peak values among a predetermined number of sampled signals output from the analog-to-digital converter, and calculating the average of the peak values; a multi-threshold detector for outputting a signal indicating a change in gain to its first output end, and a signal controlling a step size of the gain to its second output end, according to the output of the peak detector and averager; and a gain regulator for determining the step size according to the output signal of the second output end of the multi-threshold detector, and controlling the gain according to the determined step size and the output signal of the first output end, to output the controlled gain to the multiplier.
According to still another aspect of the present invention, there is provided a narrow-band noise remover for removing a narrow-band noise from an input signal to which a narrow-band noise is inflowed, comprising: a first delay for delaying the input signal by a predetermined period; an adaptive filter for modeling the delayed signal; a switch controller for determining that the narrow-band noise is inflowed if the output value of the adaptive filter is higher than a predetermined level, and turning on a switch to output the output value of the adaptive filter; and an adder for subtracting the output value of the adaptive filter, input when the switch is turned on, from the input value.